Go through your plugins like esmi said and see if there’s one specific one that’s causing an issue. I also suggest using a caching plugin. I tried the link you provided and the site would not load at all for me. As your site’s traffic increases so does your over all load on the server, this is why a caching plugin is so important.

I even tried loading a cached copy of your website and that seemed to take forever to do as well. You can always use a site like: